OBJECTIVES: To examine the benefits of a guideline-based educational program to improve management of unstable angina pectoris (UAP) in hospital patients. DESIGN: Randomised controlled trial. SETTING: 37 public hospitals across New South Wales. PATIENTS: 1,872 patients admitted with a diagnosis of UAP between 1 February and 30 June 1996 (baseline survey), and 1,368 patients with the same diagnosis admitted between 1 July and 31 December 1998 (follow-up survey). INTERVENTION: Educational sessions run by local opinion leaders, presenting guidelines on management of UAP from the National Health and Medical Research Council and feedback on local practice using data from the baseline survey. Sessions were run between March and June 1998. MAIN OUTCOME MEASURES: Use of evidence-based practice, identified by review of medical records. RESULTS: Use of beta-blockers increased in intervention and control hospitals, although the increase was significant only in the former. Use of calcium-channel blockers decreased significantly in both intervention and control hospitals. However, the change in drug use between baseline and follow-up did not differ significantly between intervention and control hospitals. CONCLUSIONS: Despite some appropriate changes in drug use for UAP management between 1996 and 1998, there was no evidence that a guideline-based educational program was of benefit in changing management. This reaffirms the difficulty of changing doctors' behaviour through practice guidelines. Alternative methods of encouraging evidence-based practice should be considered.